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    Re: Don't do this to a sextant
    From: Alexandre Eremenko
    Date: 2006 Nov 7, 20:21 -0500

    
    Dear Henry.
    
    1. Mercury seems to be available on the Internet.
    Just type "mercury" on Google and you will find several
    dealers which sell it. For about $100 per pound.
    
    2. I have instructions, how to re-silver mirrors
    from some old Navigation
    book (about 1909) but this was not Bowdich.
    
    3. I just thought you can share some personal experience,
    it is always better than an instruction in a book.
    
    4. I suppose that ordinary commercial glass
    and household mirrors are not appropriate.
    The glass for sextant mirrors has to be very flat and its
    surfaces very parallel.
    That's why I am talking about re-silvering existing
    mirrors rather than making new ones.
    I mean using glass from old sextant mirrors.
    
    Alex
    
    On Tue, 7 Nov 2006, Henry C. Halboth wrote:
    
    >
    >
    > Hi Alex,
    >
    > I have, in the past, successfully re silvered mirrors in accordance with
    > the directions in the 1909 Edition of Bowditch which do require the use
    > of Hg. The later editions of this publication do not contain these
    > directions, but I feel sure that some of the other earlier ones must
    > include them. Until recently, I had some Hg in stock but frankly do not
    > know where to buy it commercially these days; perhaps the lab at Perdue
    > could supply you. At one time all the nautical instrument houses were
    > able to handle mirror re silvering, the last I know of being New York
    > Nautical Instrument, on Hudson Street in NYC. I recently spoke with the
    > proprietor of a glass shop that also supplies mirrors commercially, who
    > offered to cut mirrors for me to any size desired, but that, of course,
    > did not include the split mirror generally employed as a horizon glass in
    > the average instrument, but cannot speak to the optical quality of
    > commercially made general purpose mirrors or their suitability for use in
    > our instruments - this later might be a subject for ongoing discussion,
    > as I would like to explore the use of mirrors as an alternative to Hg or
    > oil as an artificial horizon reflecting surface. If you do not have
    > access to a pub containing Hg re silvering instructions, I will be
    > pleased to post them, as they are not lengthy.
    >
    > Regards,
    >
    > Henry
    >
    > On Mon, 6 Nov 2006 21:05:58 -0500 (EST) Alexandre E Eremenko
    >  writes:
    > >
    > >
    > > Dear Henry,
    > >
    > > On Mon, 6 Nov 2006, Henry C. Halboth wrote:
    > >
    > > > As long as there is no deformation, I believe restoraton to a
    > > condition
    > > > of serviceability is entirely possible. I have done so with
    > > several old
    > > > sextants/octants that have been missing a variety of parts
    > >
    > > Do you make/resilver mirrors yourself?
    > >
    > > I am currently shopping for an old vernier sextant,
    > > mostly paying attention on the state of the arc,
    > > frame, vernier and filters.
    > >
    > > The requirement that mirrors should be also in good condition
    > > substantially narrows my choice. So I thought of trying to
    > > learn how to resilver mirrors myself.
    > > Can you give any advise on this?
    > >
    > > I have in mind a recipe from an old navigation book
    > > which requires mercury and tin foil.
    > >
    > > Alex.
    > >
    > >
    > > >
    > >
    >
    >
    > >
    
    
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